Rehydrate the black mushrooms in a bowl of hot water. Do the same for the rice vermicelli in another bowl, then chop them. Rinse the mushrooms well once they are rehydrated and soft.
Place the chicken cutlet, carrot, garlic, onion and black mushrooms in the food processor. You can also chop everything by hand.
Mix everything together in a bowl, then add the soy sauce, nuoc mam, chopped rice vermicelli, mung beans, chopped mint and cilantro, and egg.
Stir to combine, then add the breadcrumbs, salt and pepper to taste. Peel and grate the fresh ginger.
Run a rice paper wrapper under hot water for 2 seconds and place on a slightly damp cloth.
Place a small amount of stuffing on the top of the patty, then proceed with the folding process: fold in the edges, then fold the sides one after the other towards the middle. Then fold the top of the nem towards the filling, pressing lightly to release as much air as possible. Roll the nem on itself, pressing with your hand at the same time to gradually release the air.
Repeat the process until all ingredients are used up.
In a large saucepan, heat the frying oil: it's hot when you add a few drops of water and it sizzles. Place 4 egg rolls in the pan and cook for 7-8 minutes (the cooking time will vary according to the heat of your oil): the egg rolls should be very, very lightly browned and a little hard. Turn them often to ensure even cooking.
Take them out, let them cool and repeat the operation with all the other egg rolls.
Put the cold egg rolls back in 4 at a time and cook for a further 5-6 minutes (again, this will vary according to the temperature of the oil) until golden-brown, turning often. Remove to kitchen paper and enjoy!